Vortex flow meters, also known as swirling flow meters, are flow measurement devices that use the von Kármán vortex street phenomenon to measure fluid flow accurately and efficiently. Inside a vortex flow meter is an obstruction called a shedder bar placed at an angle to the flow path. As fluid passes by the shedder bar, alternating vortices are naturally formed downstream due to the interaction between the fluid flow and the shedder bar. These vortices are then sensed by a small sensing element located behind or within the shedder bar.

The frequency at which the vortices impact the sensing element is directly proportional to the flow velocity of the fluid. By utilizing the known cross-sectional area of the pipe and the proportionality constant determined during calibration relating vortex frequency to flow rate, vortex flow meters can calculate the volumetric flow rate using this principle known as the von Kármán effect. The sensing element converts the mechanical vibration caused by the vortices into an electrical signal that is processed by the meter's electronics to provide a flow reading.

Some key advantages of vortex flow meters include having no moving parts, requiring easy and low-cost installation without the need for straight pipe runs upstream and downstream, and wide flow turndown capability. They also suffer from low pressure drop and can handle clean or dirty liquids, gases, or steam flows. Vortex meters are highly versatile as they can operate reliably across a wide range of process conditions and fluids.

Vortex flow meters find widespread applications in oil and gas production, petrochemical, chemical, power generation, pulp and paper industries as well as other process industries. Common fluids measured include water, wastewater, fuels, compressed air, nitrogen, natural gas and steam. Their two-wire design also makes them efficient for power consumption. Some models offer integrated temperature and pressure sensors to provide compensated mass flow readings.

Redundant multi-sensor configurations provide the reliability needed for critical safety instrumented systems. However, their limitations include relatively low accuracy at low Reynolds numbers. Manufacturers have developed techniques such as using reducers to improve low flow measurement capability. Companies like Emerson offer high-quality vortex meters featuring all-welded construction, redundant sensors, and ability to measure varied process fluids accurately and reliably.

In summary, vortex flow meters have proven themselves as robust, cost-effective solutions for flow measurement needs across many industries. Their self-contained design minimizes installation complexity. With advances to push measurement performance even at low flows, vortex technology continues enhancing plant productivity, efficiency and safety.